Railroad cars having enclosed hoppers are routinely employed to transport lading. During discharge of the lading from the enclosed hopper, the air pressure within the cavity of the hopper may become substantially less than that of the atmosphere. The resulting difference in air pressure between the atmosphere and the interior of the cavity may be sufficient to cause structural failure of the railroad car or inhibit discharge of the lading.
The problem of a differential air pressure between the hopper cavity and the atmosphere has been addressed by use of venting devices that admit air into an enclosed cavity. Venting devices that have been employed in the prior art include that of U.S. Pat. No. 3,112,687 to Henneberger. Henneberger shows a ventilator that includes an integral base member that has a sleeve thereon. The sleeve fits into an opening on the surface of the deck of an enclosure. The sleeve has a peripheral flange which provides a lower baffle that is integral and co-axial with the sleeve and which is provided at its underside with radially spaced, downwardly extending ribs between which are grooves for receiving a sealant material. The base member is secured to a portion of the deck surrounding the hole by screws through a flange.
Another type of ventilator device is shown in U.S. Pat. No. 4,537,119 to Jarnot. Jarnot shows a ventilator that includes an annular base which has a central opening therein. The bottom surface of the base has an adhesive layer for mounting the base to a selected surface. The upper surface of the base has diametrically opposed flanges for engaging flanges disposed on the vent cover.
An additional example of prior art devices is shown in U.S. Pat. No. 4,315,579 to Martin. Martin is directed to a venting system for liquid storage tanks. The system includes a closure assembly that includes an upstanding wall which defines a vertical passageway that extends through the closer assembly. A sheet of filter material is seated across the opening of the vertical passageway. A dome shaped cover member is pivotally secured to the closure assembly to facilitate replacement of the filter material.
A further example of venting systems is shown in U.S. Pat. No. 3,515,051 to Pulcrano. Pulcrano shows a side plate structure conduit for venting of covered hopper cars. The side plate structure forms a conduit that extends along the length of the upper portion of each side of the hopper car. Air inlets are provided with respect to the leading end of the car. Openings in the side plate structure of the car communicate with the interior of the car to supply air thereto. Air is exhausted from the car by openings in the side plate of the car that communicate between the hopper and the atmosphere.
Venting systems for railroad cars are also shown in U.S. Pat. No. 3,611,905 to Brinks. Brinks shows a venting device attached about an opening in the roof of a hopper car to permit air to enter the interior of the car during unloading. The device has a horizontal portion overlying the roof and a vertical depending portion disposed over the end wall in spaced relation thereto. Replaceable screening and filtering members are included with the vent arrangement to prevent entry of foreign objects into the cavity during discharge.
The venting devices of the prior art function to admit air into an enclosed chamber. These devices, however, tend to be complex in construction. A need therefore exists for a venting device which functions to admit air into the interior of a railroad car during discharge without the complexities of the prior art devices.